Coded track circuit signaling system



Jan. 2, 1951 F. x. REES coman TRACK CIRCUIT SIGNALING sysmm 2 Sheets-Sheet 1 Filed June 15, 1944 Fllll ll-Il.

Jan- 2, F X, REES CODED TRACK CIRCUIT SIGNALING SYSTEM 2 Sheets-Sheet 2 Filed June 15, 1944 8 Mai U K {I nventor (Iltorneg Patented Jan. 2, 1951 CODED' TRACK CIRCUIT SIGNALING SYSTEM' Frank X. Rees, Chili, N. Y.,. assignor to General Railway Signal -Company,,.Rochester, N. Y.

Application. J unelfi, 1944, Serial N 0. 540,399

13 Claims.

This invention relates to coded track circuit signaling systems for railroads, and more particularly pertains to the provision of coded track circuit organizations in which protection is provided against the false clearing of a signal. in. the event of broken-down insulated rail joints.

In conventional coded track circuit signaling. systems where code pulses of different rates are. transmitted over the rails from one end of a track section to the. other. end, and where the code pulses in such track section are. alwaysof the same polarity, a suitable polarized relay is employed at the code receiving end of the track section which will respond only to the. particular polarity of the code pulses in: that section. Then each successive. section can have the polarity of its code pulses reversed with respect to the polarity of the code pulses of the preceding section, so that in the event of a broken-down insulated rail. joint, the. feeding of energy from a rear section to the forwardsection will not cause response. of. the polarized track relay of such forward section.

However, in certain applications of coded track. circuits to the control of block. signals, it has been found expedient to employ code. pulses. of opposite polarities alternately in. each. track. section with suitable means at the receiving end of the track section responsive to both polaritiesof current, as shown for example, in. my prior application Ser. No. 466,151 filed. November 19,, 1942, now Patent No. 2,399.7 60, dated May '7, 1946. Such a coded track circuit is highly desirable since it provides uniform operation. under variable ballast conditions, provides for better train shunting characteristics, avoids the socalled storage battery effect, and provides, oth. er advantages which will not be discussed in detail.. In a system using this type of coded track circuit, a track relay is provided at the receiving. end of. each track section which relay is of the magnetic stick type so as to require code pulses of opposite polarities alternately in order to be operated to its opposite positions. In such a system, it will be apparent that the polarity of code pulses applied to the adjacent track sections cannot be alternated with any useful result, since the track relay employed responsive to both polarities.

More specifically; it can be seen that should insulated rail joints break down in such a sys tem, the code pulses from the code transmittingmeans connected across the track rails of the. section in the rear of a signal would act-to apply code pulses to the code receiving means for the forward track section, whichv in turn would cause the associated signal to give a. proceed indication in the absence of legitimate code pulsesin the forward section. In such an event, the decoding apparatus thus clearing the associated signal would also act to change the code rate for the track. section in the rear; This increase in. code rate would be received by the forward track sectionv and cause the signal to display a still.

less restrictive indication, and would in turn cause a still different code. rate to be applied to the section in the rear. In other words, without proper broken-down joint protection, it would be possible for the breaking down of the rail. joints at a signal location to cause a progressive self-clearing of that signal.

In view of the desirability of employing codedtrack circuits having code pulses of. alternate polarities, and in view of the above. describedpossibilities, one objectof the present invention is to provide a means. associated. with such. codedtrack circuit apparatus as to prevent the false clearing of a signal in the event of av brokendown insulated rail joint.

A- further feature of the present invention. is taso. organize the protective means that a distinctive. indication of a signal will be given, such as a. flashing indication, to thus advise traincrews. or maintenance men that a broken-down joint condition exists so that it will be quickly repaired without. undue delay of train .movements.

, .A still further feature of the present invention is? to so organize the broken-down joint protective features that the breakingv downv of insulated rail. joints at one signal location will causethe display of adistinctive indication at the signal. next in. the rear, but in so doing doesnot. cause. the. condition to be. cascaded to the second signal. in the rear.

To provide a coded track circuit organization capable. .of. accomplishing the above objects, it is convenient. to employ decoding apparatus which requires a predetermined time to respond upon the. cessation. of a code ina track section before it. assumes such a condition as to causev the code rate in. the. adjacent. section in. the rear. to. be changed to a. different code rate to thereby prevent certain transitory conditions] from. being, cascaded from one sectionv into another during. a. broken-down joint condition. Thus, if such predetermined time were. effective upon. the entrance of a. relatively short, and, fast travelling, train into a section, the train might wholly enter the track section before such predetermined time would have elapsed, and to allow a clear code to exist momentarily in the rear section. In view of such a circumstance, it is proposed to provide means initiated upon the approach of a train to a signal location and efiective for a. time after its entrance into the forward track section, to render the decoding apparatus at the signal location more quickly responsive than said predetermined time to the cessation of the code upon the entrance of that train into the forward track section, so that the most restrictive code rate will be transmitted in the rear track section prior to the elapseof said predetermined time. Thus, regardless of whether a train is of the usual length or is a relatively short train, the decoding apparatus responds sufficiently quickly upon the passage of that train as to prevent the momentary transmission of a clear code, while under other conditions when a train is not present, the decoding apparatus is relatively slow to respond in accordance with said predetermined time.

Other objects, purposes and characteristic features of the present invention will be in part obvious from the accompanying drawings, and in part pointed out as the description of the invention progresses. detail, reference will be made to the accompanying drawings, in which like letter reference characters are made distinctive by the use of distincu tive preceding numerals characteristic of the different signal locations of the block signaling system disclosed by the present invention, and in which:

Fig. 1 shows a block signaling system employing coded track circuits having the broken-down insulated joint protection characteristic of thepresent invention; and

Fig. 2 shows a modified form of the invention disclosed in Fig. 1.

For the purpose of simplifying the illustration and facilitating in the explanation, the various parts and circuits constituting the embodiment of the invention have been shown diagrammatically and certain conventional illustrations have been employed, the drawing having been made more with the purpose of making it easy to under-- stand the principles and mode of operation, than with the idea of illustrating the specific construction and arrangement of parts that would be employed in practice. Thus, the various relays and their contacts are illustrated in a conventional manner, and symbols are used to indicate connections to the terminals of batteries of other sources of electric current instead of showing all of the wiring connections to these terminals. The symbols and are employed to indicate the positive and negative terminal respectively of suitable batteries, or other sources of direct current; and the circuits with which these symbols are used, always have current flowing in the same direction. (3-) indicate connections to the opposite terminals of a suitable battery, or other direct current source which has a central or intermediate tap designated (CN) and the circuits with which but it should be understood that the signaling system of the present invention contemplates the In describing the invention in' The symbols (3+) and use of any desired number of track sections. The track section IT is separated from section 2T by insulated joints 5; while the track section 2T is separated from the track section 31 by the insulated joints 6.

At the entrance to each track section and adjacent the insulated joints, a suitable signal is shown as comprising two Searchlight type signals, which may be of any suitable type such as shown in the prior patent of O. S. Field, Pat. No. 1,835,150 dated December 8, 1931. These upper and lower arm signal mechanisms have been'shown, so as to illustrate how a multiple number of signal indications may be given in connection with a systememploying the present invention. However, it should be understood that color light signals, or any other suitable signals may be employed and that only three indication signals may be used if desired.

These signals 2 and 3 are controlled in accordance with the codes applied to their respective track sections so as to give a green over green (G/G) indication upon the reception of a 180 code rate; to give a yellow over yellow (Y/Y) indication upon the reception of a 120 code rate; to give a yellow over red (Y/R) indication when a '75 code is being received; and to give a red over red (R/R) indication upon the absence of all code.

Each track section of the proposed signalling system is supplied with similar apparatus, so that the description pointing out in detail the apparatus associated with the track sections shown in the drawings will give an idea of the apparatus associated with the various track sections throughout a stretch of track equipped with a block signaling system as contemplated in accordance with the present invention.

More specifically, ,the track section 2T is provided with a track relay 2TB which is indicated as being of the two-position magnetic stick type, that is, its contacts are operated to opposite positions upon energization of the relay with current of opposite polarities, and remain in their last actuated positions until the relayis energized with, the opposite polarity. The track relay 2TB which through suitable detuning apparatus causes the contacts of a neutral relay 2BH to be picked up whena code of the 1.20 rate is being received, and similarly causes a. relay 2D to be picked up whenever a code of the 180 code rate is being received. Although these relays 231-1 and 2D are picked up only when their respective code-rates are being received, a home relay 2H is picked up whenever the code rate 01' any other higher code rate such as or is being received. Although therelay 2311 is picked up in response to the operation of the track relay ZTR only upon the reception of the 120 code rate, it is caused to be picked up whenever the relay 2D is picked up by means of local circuits. More specifically, front contacts I and 8 of the relay 2D provide an obvious local circuit for the relay ZBH.

.Each of the signal mechanisms is provided with a signal repeating relay which is energized only when the associated signal mechanism is displaying a yellow or green indication. For example, the relay 2AYGP is picked up whenever the signal mechanism 2A indicates yellow or green;

and continued similarly, the relay ZBYGP is picked up whenever the signal mechanism 23 indicates yellowor green. The yellow-green repeating relays AYGP for the upper arms of the various. signals are of the slow pick up slow release type for reasons :later i'explained. (Dn'the other hand, the yellow-green repeating relays BYGP for the lower arms of the signals are merely of the slow'release'type.

Each signa'l locationhas a repeatingrrelay VR which is employed to repeat the lower arm yel- IOWegreenrepeating relay BYGP andthe distance relay D, and this relay controls the associated signal mechanism so as to cause them to display green indications only after the lower arm has displayed ayellow indication and the uppersarm is receiving a green control.

The code receiving and signal controlling means, above described, is of course typical :of the apparatus associated with the entering end of each track section, and each such receiving apparatus is governed by codes transmitted from the leaving end of its track section. Each code transmitting means at the leaving end o'f a section transmits codes of different rates 'asselected by the condition of the code receiving "apparatus of "the next adjoining track section-in advance.

For example, the signal location 2 has associated with the leaving end of track section IT, a code transmitting relay ICP which is 'of the two-position polarized magneticstick type so as to remain in its last position until e'nergized'to an opposite position. Thisrelay lCP acts'to apply impulses of opposite polarities to the associated track section from a battery IE or some other suitable source of current, for very short intervals of time measured by a repeater timing relay ICPT. The relay HOP is actuated to its opposit positions at the selected code rate -by suitable code oscillators 0r coding contacts designated 150, I200 and IBQC, and each time the relay ICP is operated to its opposite position "a change in polarity on the relay I CPT'cause it to be momentarily dropped away to apply through back contact if a momentary impulse to the track circuit IT, which impulse has a polarity determined by the position of contacts H and 12 of relay ICP.

The code transmitting apparatus "associated with the leaving end of a track sectionalso includes approach control means, that is, means which is responsive to an approaching train for governing the approach lighting of the associated signal, and for governing the code "transmitting means as will be hereinafter described in detail.

For example, an approach track relay "IAP, of the two-position polarized magnetic stick type is connected across the rails of the track section IT and is operated to its opposite positions alternately as codes of different rates are applied to the track section by the code transmitting relay ICP. This following of the code applied to'the track section by the approach relay lAP continues only until a train enters the track section. Such entrance of a train into the track section IT of course shunts the two rails of the'secti'on causing a higher current to flow from the battery IB, and this higher current flow includes theresistor lR'so that the potential drop 'acrossthe track rails at the leaving end is subStaLntiall'yflr'edu'ced'below the operating'value of the relay I This cessation of the operation of the'relay 'IAP results in the deenergization of its repeater relay IAPR, which in turn effects the approach lighting of the signal and the desired control of the'code transmitting apparatus.

It'should'be noted that the rela'ylAPR picks u'p'its contacts in response to the operation'of contact 29 at any of the selected code rate'SQbut if the contact 2 9 remains in either position, "the contacts 'of the relay IAPR .drop'away. @is due to Fthespecial"constructionsof :the rrelaywhich has been fully disclosed in my 'prior application Ser. No. 469,346 filed December 17, 1942, which has .resulted in .Patent No. .2,390;666,jdated-December 1 11, 1945, but it is to be understood that this spe'ciallyconstructed decoding relay does not necessarily have to be employed in order'to practice this invention, "since one or more slow acting repeating srelays, or any othersuitable decoding means, may be employed for decoding purposes.

It I is .believed that the present invention would be best understood by further description being given from {the standpoint of operation.

Operation of Fig. .1

Underf normal conditions with no trains in the stretch, codes of'the 180 rate are of *course being transmitted to each of the track sections causing each of the signals to indicate With ref erence to the drawing it will "be seen that the operation of contact :34 of track relay r3TRiat the 180 code rate will act through'the associated decoding transformer and rectifying contact to :control the relays 3H and 3D under such-normal coding conditions to their picked up positions. 'The'relay 3D in closing its "front contacts l3 and nets to energize the relay 33H through an "obvious local circuit.

Although it is necessary for thesign'al indications to be built up, so to speak, in a particular sequence as will be described later, it is sufiicient for the present to point out the energizing'circuits for the signals under the normal conditions mentioned disregarding for the moment any sequence with respect to the order in which such circuits are completed.

With the signal 'mechanism 3A operated to a green indication position, an energizing circuit is closed from through a circuit including contact l5 of signal sA, frontconta'ct l6-of relay 3H, windings of relay 3AYGP, to Similarly, the signal mechanism 33 isalso operated to-a green indicating position which closes contact l to supply energy from through front contact 18 of relay 3BH, to the windings or relay 'SBYGP, to With relays 3BYGP and 3D' both picked up, a circuit is also closed from through front contact is of relay SBYGP, front contact 2!] of relay 3D, windings of relay 3VR, to

"The energizing circuit for the'operatin winding of sign'al'mechanism 3A'is closed from through a circuit including front contact 21 of relay 3VR, front contact 22 of relay 3H, operating winding of signal 3A, front contact 2-3 of relay 3H, front-contact 2 50f relay 3VR, to

'The operating winding of signal mechanism 3B 'is energized from through a circuit including front contact 21 of relay BVR, front contact 22 "of relay 315, front contact 25*of relay 3AYG'P, front contact 26 of relay SBH, operating coil 'of signal 3B, front contact 21 of relay BBH, front contact 28 of relay GAYGP, front contact 23 of relay 3H, front contact 24 of relay 'VR'to "With the signal 3 thus displaying'a 'G/G indication, the code transmitting relay 2GP is alternately receiving energy in opposite directions at the code rate from (B+) and (B') throughcontact'sil of the coder I800, front contact 3! "of relay SBYGP, front contact 32 of relay sHffront contact 33 of relay 3AYGP,jwind-" ings of relays 2GP, to (CN). This operation ofthe rlayYCP to'opposite positions alternatelyoperates its contacts M and 42 to opposite posi-' tions to momentarily energize the track section 2T with successive code pulses of opposite polarities alternately, each impulse being applied while the back contact 40 or relay 2CPT is closed. This relay ZCPT i energized with the opposite polarity each time contact 43 of relay 2GP assumes its opposite position. This reversal of the direction of current through the windings of the relay 2CPT causes the magnetic flux in the core of that relay to pass through zero and when this occurs, its armature momentarily drops away.

The application of the 180 code to the track section 2T of course causes the signal mechanisms 2A and 2B to be operated to G/G indicating positions in a similar manner as described in connection with signal mechanisms 3A and 3B.

Passage of a train.Assuming that a train is approaching the signal 2 over track section IT,

it will be apparent that the approach track relay IAP ceases operation so that its contact 29 remains in one position and thus cause the approach repeating relay IAPR, to release its contacts. The closure of the back contacts 64 and 65 of relay IAPR energizes the lamps of the signal mechanisms 2A and 2B respectively so that the signal 2 displays the G/G indication. The opening of front contact 66 of relay IAPR accomplishes no particular function at this time, but the closure of back contact 56 prepares a circuit for causing the transmitting relay ICP to be energized in accordance with the 75 code rate in a manner presently to be described.

Since the signal 2 is displaying a G/G indication, the train may proceed at the regular speed past such signal location. When the train enters the track section 2T, it shunts the track rails so as to cause the track relay ZTR to cease operation. Thus, the relays 2H, 2BH, 2D and 2VR drop away causing the operating windings of the signal mechanisms 2A and 2B to be deenergized so that their spectacles assume red dis playing positions. With the relay IAPR still dropped away, the signal 2 continues to display a R/R. indication.

Since the relay 2H is only slightly slow acting, that is, sufficiently slow to remain picked up during the reception of even the slowest code rate, but acting to drop away almost at once upon the cessation of a .code in the track section 2T, it assumes a released position somewhat prior to the release of the slow releasing relay ZAYGP. This is in part due to the fact that the relay ZAYGP cannot begin dropping away until after the front contact 55 of relay 2H has opened. The opening of front contacts 50 and 5! of the relay 2H deenergize the signal mechanism operating windings as above mentioned, while the opening of front contact 44 disconnects the code transmitting relay ICP from the coder I300 and connects the code transmitting relay ICP through back contacts 44 and 66 to the coding contact 45 of the coder C. Then upon the release of the relay ZAYGP and ZBH, the latter relay being deenergizedfollowing the release of the relay 2D, the code transmitting relay ICP is energized with (3+) and (B) alternately through a circuit including contact 45 of the coder 15C and back contacts 61, 48 and 49 of the relay 2H, 2BH and ZAYGP respectively. In other words, the codin transmitting relay ICP is energized with the most restrictive code rate as soon as the relay 2H releases in spite of the fact that the relay orrelay 2H. This relay ZAYGP being slow to pick 2AYGP does not release at the same instant as' the relay 2H.

Assuming that the train has wholly entered the track section 2T, this code transmitted to the rear of the train over the track section IT is of the 75 code rate and causes the next signal in the rear to have its mechanisms operated to Y/R indicating positions. In this way, the track section to the rear of a signal is immediately energized with the restrictive code rate upon the passage of a train into the track section in advance of such signal, and this occurs during an interval of time sufliciently short to prevent a momentary transmission of a clear code rate in the rear of the train even though such train is extremely short. In other words, a short train cannot leave the track section IT and wholly enter the track section 2T in the relatively short time required for the deenergization of the relay 21-1. The significance of this inclusion of the contact 44 in the code selecting circuit with the relay IAPR. dropped away, and the exclusion of this contact 44 in such code transmitting selecting circuit when the relay IAPR. is picked up, will be discussed in greater detail hereinafter.

The entrance of the train into the track section 2T of course causes the approach relay 2AP to cease operation for reasons previously mentioned, which in turn causes the contacts of the relay ZAPR to be released for approach lighting the signal 3 and afiect the code selection circuits for the coding transmitting relay 2GP in the same way as described in connection with the passage of the train past the signal 2.

When the train proceeds past the signal 3 into the track section 3T, the relays 3H, 3BH and 3D are similarly cleenergized and a code of the I5 code. rate is applied to the track section 2T in a similar manner as described in connection with the track section IT. This circuit for the relay 2GP includes contact 46 of the coder 15C and back contacts 68, 69 and 33 of the relays 3H, 33K and SAYGP respectively. The reception of this 15 code at the signal 2 is repeated by the track relay 2TB and causes the contacts of the relay 2H to be picked up. It is assumed that under these conditions there is no train approachingv the signal 2 so that the approach relay IAPR is picked up by the 75 code being applied to the track section IT through back contacts 61, 48 and 49. Thus, the picking up of the contact 61 of the relay 2H shifts the control of the relay ICP from the contact 45 of the coder 15C to the control of the contact 47 of the track relay ZTR. Thus, the track relay 2TB. applies (B+) and (B-) alternately to the relay ICP through a circuit including front contact 6'I'of relay 2H, back contact 48 of relay EBH, and back contact 49 of relay 2AYGP. In this way, the '75 code rate is continued to be applied to the track section IT after the relay 2H is picked up. This continues until the relay ZAYGP is picked up after the sig nal mechanism 2A has been operated to a yellow indicating position.

More specifically, the closure of the front contacts 50 and BI of relay 2H applies energy to the signal mechanism 2A through back contacts 52 and 53 of relay ZVR, and the energy flows in such a direction as to cause the signal mechanism 2A to operate to a yellow indicating position. The operation of the mechanism 2A to such a position closes contact 54 which completes a circuit for the relay 2AYGP through front contact 55 up, closes its front contacts after a time and shifts the circuit for the relay lCP through front contact. 49 of relay 2AYGP, front contact 44 of relay 2H, and back contact 56 of relay ZBYGP so that it is energized at the 120 code rate from the contact H! of the. coder i200. This of course causes the 120' code rate to be applied to the track section IT while the train is in the track section 3T, to thereby cause the mechanisms of the signal next in the rear of signal 2 to be operated to positions for displaying a Y/Y indication.

It is desired to point out here that under this normal operation at the signal 2 when a train enters the track section ET, the code transmitted over the rear track section iT is dependent upon the reception at the signal 2 of a proper code over the track section 2T for a period of time subsequent to the picking up of the relay 2H equal to the response of the signal mechanism 2A and the picked up period of theslow pick up relay ZAYGP'. As a matter of fact, the transmission. of the code in track section IT during this period of time is a direct repeating of the code from track section 2T.

Assuming that the train proceeds from the track section. 3T into a successive track section 4T (not shown), a 75 code rate will be appliedto the. track section 3T which will be received at the signal 3 to cause it to be operated to a Y/R indicating position, and at the same time cause a 120 code rate to be applied to the leaving end of the: track section 251.

The reception of the 120 code rate at the. signal 2 will of course result in the: picking up of the relay ZBH to close front. contacts 51- and- 58 and thereby complete the energizing circuit for the signal mechanism 2B; it being understood. that front contacts 59 and 60 of the relay 2-AYG'P arev already closed. However, the current inthe operating winding of the signal mechanism: 25 is of such a direction with relay ZVR deenergized, as to cause the spectacle of the signal mochanism 23 to. be. operated to a yellow indicating position, This closes contact 6|: of the signal mechanism 23 which. completes an energizing, circuit for relay ZBIYGP including front contact. 2 of relay ZBH The picking upof relay iBlYGP closes front contact 56 and shifts the control of the. code transmitting relay CE from the con tact of the coder [20C to the contact H. of the coder I800, so that a 180- code is applied to the track section lT; In this waythe signal next in. the rear of signal 2 is caused to display a G/G indication.-

Assuming that the train proceeds. through. the stretch. and enters the next successive track. sectionso that a 120 code is applied to the track section 3T and a 180 code is applied to the track section 2T, it will be seen that the relay 2D is caused to be picked up in response. to. such code and the closure of its front contacts 7 and. 8 will act to maintain. the relay ZBH picked up .through a local circuit in spite of the fact that such relay would ordinarily drop in the absence of the 120 code rate. Since the relay ZBYGP is already picked up, a circuit is now closed; for the relay'2VR from (-1 and including. front contact 74 of relay ZBYGP, front contact of relay 2D, windings of" relay ZVR, to (-1. This, picking up of. the contacts. 52 and 53 of relay ZVR merely reverses thezdirection of current flow in. the operating windings of the signal. mechanisms 2A and so that their spectacles are moved fromtheir yellow indicating, positions to green. indicatin positions to thereby cause the sign r a 9 pg 1G ready to display a G/G indication upon the approach of a train.

Broken-down insulated joint protection-Although the insulated joints of the usual type and construction may gradually lose their insulating qualities and permit a low resistance leakage path to develop around these joints over period of time independently of train movement, it generally happens that a broken-down joint condition is created as a, result of train movement over the joints; and since it is the presence of a train which makesit' unsafe to display a wrong signal indication, it is convenient to discuss the operation of the invention on the assumption that the insulated joints are broken down by the train movement.

As a typical example of the contemplated operation under such circumstances, let us assume that a train traveling inthe normal direction of traffic, that is, from left to right in the stretch of track shown in the drawings, and that, as the train passes the signal location 2, the insulating joints 5 break down. So long as the train is effectively shunting the rails of the track section 2, no harmful situation arises since the shunting action of the wheels and axles of this train prevents the operation of the track relay ZTR. due to any energy that may leak around the insulated joints from the track section 3T. However, as the train progresses through the track section 2T its shunting effect may become poor due to defective bonding of the rails, a broken rail or the like, and thus sufficien't energy will pass around the joints 5 to cause the operation of the relay 2TB although track section ET is actually occupied.

Under such circumstances, co'de pulses of the code rate are applied to the track section l T by the code transmitting relay lCP' by reason of its connection through back contacts 43, 8 and 6:? to the contact 45' of the coder 5'50. As"- suming that these impulses leak around the damaged joints 5 and cause the operation of the track relay 2TB, the relay 2H of course picksup opening back contact 9-1 and closing -ltront contact 81. This closure of front contact 6! while back contacts it and 5'9 are still closed (due not only to the time required for operating the signal mechanism LA. but also due to the slow pick up characteristics of relay ZAYG'P) conmeets the" relay ICP' to the contact W of the track relay Z-TR as previously described. This connection, however, cannot cause the operation of the relay lCP, because the track relay 2TB in closing its front contact 4'! in response to the operation of the contacts of relay lCP being operated toa: particular position, energizes the code transmitting relay I CP' with such a polarity as to -maintain its contacts in that particular'positi'on, Thus, a locked up condition is produced. In other words, the track relay 2TB ceases ope'ration and: the relay 2H drops away before the .rel'ayzAYGP can pick up and supply energy to the transmitting relay lCP from coder contacts.

As soon the relay 2H- dr'opsaway and closes back contacttl, the code transmitting rela I CP is again operated from the contact 4'5 or the coder 156 This: alternate? operation and cessation of operation-of the code transmitter I CP is continued so long as. the assumed conditions exist; In other words, a, proper build up of the coderate. cannotbe effected in the track sec- ,tion in the rear of a signal. location where: the

joints are broken down because the; usual: re-

peat connections cause a temporary locked-up 11 condition and thereby prevents a shifting to the next higher code rate in the proper sequence of operation.

This alternate picking up and dropping of the relay 2H causes the signal mechanism 2A to be alternately operated to a yellow indicating position and returned to its stop or red indicating position. Such operation of the signal does not, however, allow the relay ZAYGP to pick up. If a train should approach the signal 2 under the assumed condition, its wheels and axle would shunt the rails of the track section IT causing relay IAP to remain in its last operated position. Also, the shunting of the track rails of section IT would be efiective to also prevent operation of the track relay 2TB although the code transmitting relay ICPT would be operating at the 75 code rate. With the back contacts 64 and 65 of the relay IAPR. closed during the approach of such train, the signal 2 would then be caused to display a R/R, indication. This properly stops such approaching train under the adverse conditions assumed where a train is occupying the track section 2T but is failing to properly shunt the track relay ZTR due to a broken rail or broken bond wires or the like. a

In order to understand what happens to the approach signals under such a situation, it is convenient to assume that the insulated joints 6 are broken down and that the insulated joints 5 are in good condition. We should also assume that a train has passed through the track section 3T to a. point which falls to shunt the track relay 3TR so that there is an intermittent application of code pulses of the 75 code rate to the track section 2T in a manner similar to that described above in connection with the 'track section IT. In this connection, it should be understood that there are at least two possibilities of different resulting operations depending upon the degree to which the insulated rail joints are broken down.

In the first case, it may be that the joints 6 are very badly broken down thus producing a very low resistance path between the two track sections, in which event th train in track section 3T not only shunts that track section 3'1, but also continues to shunt the track section 2T until it passes through the track section 31 up to the point where it ceases to be an efiective shunt due to a broken rail or the like. In this case, there is no code pulses in the track section 2T until the operation of the apparatus at the signal 3 begins to apply a code of the 75 code rate at spaced intervals as above described for a broken joint condition.

On the other hand, it may happen that the joints 6 are only broken down to a limited degree so that when the train enters the track section 3T, there is an application of the '75 code to the track section 2T in the usual way which is efiective to operate the track relay ZTR continuously until the train in the track section 3T passes beyond a broken rail 01' the like, and no longer shunts the track relay 3TB which begins to follow the code pulses applied by the relay 2GP and thus causes the intermittent application of a code of the 75 code rate to the track section 2T. From this it can be seen that the degree to which the joints 6 are broken down will somewhat determine the operation under any given situation.

Since the joints do not usually break down rapidly, the latter or second case mentioned above is usually the situation to occur, in view of which it will be discussed first. It is assumed that the train just passed the joints 6 and caused a continuous application of the ,75 code for a limited time to the track section 2T which was effective to pick up the relay 2H, cause the signal mechanisin 2A to be operated to a yellow indicating position and efiect the picking up of the relay 2AYGP. Such operation of course shifts the control for the relay ICP to the contact 10 of coder I200 by reason of the closure of front contacts 49 and 44 while back contact 56 is closed. Then as soon as the intermittent application of the code to the track section begins, the relay 2H intermittently drops away and picks up in synchronism, so to speak, with the relay 3H, but the relay ZAYGP being slow releasing does not have sufiicient time to drop away.

Although the front contact 44 of the relay 2H is intermittently opened and closed, it should be noted that the front contact 66 0f the relay I APR provides a connection from back contact 44 to the heel of contact 56, and thus in effect shunts the contact 44 out of the selecting circuit for relay ICP since the time of operation of contact 44 from a front point to a back point is of no practical bearing on the continuity of the control of the coder I20C over the code transmitting relay ICP. For these reasons, the code is continuously applied to the track section IT. Therefore, the breaking down of the joints 6 and the provision of the broken-down joint protection afforded by this invention does not cascade into the preceding track section of the stretch.

A train may then properly proceed up to the track section IT and then cause the release of the contacts of the approach relay IAPR to illuminate the signal 2 and since the relay 2H is being intermittently picked up and dropped away, the signal 2 will display Y/R and R/R indications alternately. This advises the approaching train that the next signal inadvance will be displaying a R/R indication and that such indication is due to an abnormal trackway condition.

the track section 2T, the relay ZAP is caused to drop away, as-previously described, to approach light the signal 3. This shunting of the track rails of the section 2T also causes the potential across the rails to drop due to the increase of current flow through the resistor 2R, so that the track relay 3TH. also ceases operation, which of course causes the relay 3H to remain deenergized. For this reason, the signal 3 displays a. R/R indicat on, and thereby properly protects the rear of the train which is still standing in track section 3T under the conditions assumed.

Under the conditions where the insulated joints 6 are completely broken down, as above mentioned, the entrance of a train into the track section 3T con+inues to shunt the track section 2T as well as the track section 3T so that there is no period of continuously energizing the track section 2T with the 75 code, before the intermittent energization of the track section 2T with the '75 code occurs following the passage of the train in the track section 31 to such, a point where it ceases to be an effective shunt for rea-'- sons above discussed. In other words, the track relay ZTR begins to be operated in accordance with the intermittent application of the 75 code and the relays 2H and 3H are alternately picked jup and dropped away in synchronism immediately following the condition of no code in track section 2T. However, under such circumstance *the relay 2AYGP has not been picked up, nor is it energized for a suiiicient period of time to characteristics:

13 client.- itsr picking; up because of its; slow: pick up This: causes, the track section I I. to alsohave the:.7.5 codezintermittently applied to-it, because each timethe: relay 2H. picks up, the relay ICE is disconnected. from. the coder. 15C andconnected to the track relay contact 41 which has ceased. operation at that: time. However, at the. signal location I- nextin the rear but not shown, the relay: AYGP has'been pickedup dueto .mitting relay. for the track. section next; in the rear. However, if such intermittent: code; should ceasev entirely, such condition would be repeated by the release of slow pick up-slow release relay AYGP;

In other words,.the-.norma-lpassage of a train through the. successive track sections: causes. the most. restrictive.- code. (7-5. code) to be applied. to each. track section in.- successionintherear of the train. Such 75-code causes the slow: pick up relay- A YGE to: be picked up. after; a. time during which the repeat circuit at: the track section: is brought into efiect, so that the code transmittingv relaycircuit'for. the adjacent section is selected: through contacts of theI-Ii relay, but after therpick'up of the relay-AYGP hasbeen efiected, the contacts of the H relay are excluded from the circuit for the associated code transmitting relay. Thus, the occurrence of an intermittent code transmittingcondition; such as occurs during abroken-down joint condition, is ineifectivc to be repeated into. the nexttsectionin the rear of a signal because of the slow release-characteristics of the associated rel'ay AYGP; since the contacts of the: associated H relay have been ex:- cluded from the code-rate selecting circuits. In this way, the slow releasin characteristics of a relay are. employed to mask out the intermittent transmission of a code, While at the same time retaining the relative quicl -acting characteristics of the H relay'byusing'the approach control relay tore-insert its contacts into the code rate selecting circuits-upon the passage-ofa train.

Passage of dshort train.As' above mentioned, the'contacts of the H relay areexclud'ed from the code rate selecting circuit by the associated approach relay, but when a train is approaching the signal; these contacts: are re-i'nserted' into the control of the code transmitting relay. More specifically, the contact 44 of the relay 2H is efiective to select'the code rate applied to the relay lrCP only when the ap roach repeating relay lA'PR' is denergized; With such approach control', a short or so-called light train may pass a signal location at-any of the usual running speeds without permitting a temporary transmission of a clear code rate.

Tia-state the situation in another way, the forward partof' a train shunts the track section 2T for example and'causes'the relay 21-1 to drop away before the rear of such train can entirely leave the track section QT and allow the freetran miss on of code in that section. This i's'loecaai eof the: time ofrelease of the decoding relay 2H is shorter than the: time required for the train to efiectivelyp'assifromone section to another. For

these reasons; it is believed that the presentinvention afiords. the desired broken: joint: protectien: together: with the efiicient. and effectivecon- .trol or". thesignals under various traffic condi- .tions;

It should perhaps. benotedthattheiront con- .tactJ-Sw of rel'ayZBl-l for example,will provide that that-relay- ICP-is controlled in accordance with; the

contact 35 of: the: coder 150 when back contact tilt of the relay ZAYGP isclosed. This circuitis provided; so as to cause the most restrictive code rate to be applied to the track section IT in. the .event that a circuit failure results in the relay lA-YGP' remaining deenergized although a (01? 180rcode is. being received by the signal 2 for example. If this circuit werenot provided there .would. be no; code rate, applied; to the rear track .sectiorrwhichwould: of ccursenecessarily stop the passage of traffic. A similar circuit is provided rat each signal location.

@rganization of Fig. 2.--This Fig. 2 is' a modi'.- fiedxform' of the invention simplifying the organication or Fi'g. l1, andtherefore the corresponding devicesand: parts have been given the same reference characters. except those contacts which areincluded in difierent selecting circuits, Each .signa-llocation has the same apparatus; aszpreviously described, with exception of theapproach relay AP and its repeater APR. which have been :omitted. Thus, the signals are shown as being steadily illuminated and displaying their G/G indications. The decoding apparatus and the signal control circuits are all the same as previously described in connection with Fig. 1, but the control of the code transmitt ng relay CP is modified in accordance with this form of the invention and therefore the description will be-di- .rected moreparticularly to this portion of the disclosure of Fig. 2 and to the bearing which it has upon the" function and operation of this form of the invention. i Operation of Fig. 2

Under normal conditions, each track section has a 180 code applied to it so that each of the signals are operated to positions to cause the dis- ;play" of their G/G indications. Thus, an ap .proaching train will view the proceed signal indication at signal 2 for example and continue into the. next track section. The entrance of a train zinthetrack section 2T causes the decoding relays 2H, ZBH and 2D to drop away, which of course re- ;stores the signal mechanisms 2A and 23 to their stop positions. This in turn cau es the deenergization of the relays EAYGP, ZB YGP and ZVR. The-closure ofback contact 26! of relay 2H causes .therelay I CPtobe governed in accordance with the coder'l EC so-as to apply a '75 code to the track section IT;

When the train proceeds into the track section 3T2 it. likew se causes the signal 3 to display a R/R indication, and also causes the code transmitting relay 2GP to be energized through back contact 262 of relay SE in accordance with the coder at its signal location. 'Ihereception of a 7.5 corle at the signal 2 is repeated by the relay 2H which in turn causes the signal mechanism to be operated to yellow displaying pos tion and this in turn com l tes the energizing circuit for the rela ZA'YGR However. during the pick-up period of there'lay ZAYGP. the front contact 2!]! of relay 2H connected 'the relayl'CP'through back contacts M23 and 254 to the contact 41 of the associated" track relay Z TR. Since a 75- code 'rate is being received at the signal 2 over the track section 2T, the relay ICP continues to operate at the 75 code rate until the relay 2AYGP picks up and closes front contact 283, at which the relay ICP is operated at the 120 code rate through back contact 205 in accordance with the operation of the coder I200.

In a, similar way, the passage of the train out of the track section 3T into the next succeeding track section (not shown), causes a 75 code rate to be applied to the track section 3T resulting in the application of a 120 code to the track section 2T which in turn picks up the relay 2BH causing the signal mechanism 213 to be operated to a yellow indicating position and effect the picking up of the relay ZBYGP. The closure of front contact 265 of relay ZBYGP shifts the control of the code transmitting relay [GP to the coder I80C. This causes the application of a 180 code to the track section IT.

From this description it will be seen that the operation of this modified form of the invention provides the same repeat feature at each signal location as provided in Fig. 1, so that when a particular signal location initially receives a '75 code, that code is for a limited time repeated directly into the next track section in the rear.

Broken-down joint protection of Fig. 2.-This form of the invention provides the same features of broken-down joint protection as provided in Fig. 1, with the exception that the intermittent transmission of a '75 code in a track section causes the atlernate operation of a 120 and a '75 code in the next track section to the rear.

For example, let us assume that the joints 6 are broken down and that a '75 code is intermittently applied to the track section 2T under assumed conditions similar to those pointed out in connection with Fig. l where a train has passed the signal 3 and is still in the track section 3'1, but at a point where it ceases to effectively shunt the track relay ETR. The reception of this '75 code at the signal 2 causes the relay 2H to be alternately picked up and dropped away in synchronism with the relay 3H at the signal 3. This is due to th intermittent operation of the relay 2GP which occurs for reasons pointed out in connection with Fig. 1. The relay 3AYGP does not pick up because such relay is slow to pick up and does not receive energy for a sufiiciently long period with the relay 3H only momentarily picked up for each successive cycle of the intermittent operation.

Assuming that the relay ZAYGP has not yet been picked up for similar reasons, then the contact 20! of the relay 2P alternately causes the code transmitting relay ICP to be controlled in accordance with the coder 15C and the track contact 41. This causes an intermittent transmission of a 75 code in the track section IT, but since a 75 code was continuously applied to the track section I T while the train occupied thetrack section 2T, the relay lAYGP at the signal I (not shown) is picked up causing the next track section in the rear to have applied to it a 120 code alternately with a 75 code.

The reception of a 120 and a 75 code alternately at the rear of the signal I (not shown) would cause the apparatus at that signal to apply a 180 code in the rear thereof.

On the other hand, if it happened that the track section 2T did receive a 75 code for a sufficient period of time to pick up the relay 2AYGP before th intermittent application of the '75 code to the track section 2T, then the picking up and dropping of the relay 211 would. shift the control of the relay lCP between the coder C and the coder C to alternately apply a 120 code and a 75 code to the track section IT. Under this circumstance, the reception of the 120 and '75 code alternately at the signal I (not shown) would cause that signal to alternately display a Y/Y and a Y/R indication, and at the same time to cause a code to be transmitted to the track section in the rear of such signal I.

Inasmuch as Fig. 2 does not shown sufiicient track sections, to point out specifically the detail operations with respect to all track sections in the rear of a broken-down joint, it will be expedient to consider what happens at a signal location receiving a 120 code and a 75 code alternately. For example, when the signal 2 receives a 120 and a '75 code alternately, the relay 21-1 at such location remains picked up, while the relay 2BH alternately picks up and drops. Thus, the relay ZAYGP is maintained picked up, so that the intermittent picking up of relay 23H efifects the intermittent operation of the signal mechanism 2B to a yellow indicating position. Such intermittent operation of the signal mechanism 213 causes intermittent energization of the relay 2BYGP, which if it has already been picked up, remains picked up so as to close front contact 205 and eifect the continuous operation of the code transmitting relay ICP at the 180 code rate. On the other hand, if relay 2BYGP has not previously picked up, it now does so and remains picked up to efiect operation of relay ICP at the 180 code rate. This is because the relay 2BYGP is relatively quick to pick up as compared to its slow releasing characteristics, so that its intermittent energization causes its contacts to pick up and remain picked up between successive energizations. Thus, front contacts 20!, 203 and 205 are closed to cause the relay ICP to be operated in accordance with the 180 code rate from contact H of the coder I8C.

In brief, this form of the invention provides that the signal location receiving an intermittent 75 code rate as a result of a broken-down insulated joint in advance, displays Y/R and R/R indications alternately, and at the same time causes an alternate transmission of the 75 and 120 code rates in the track section to the rear. The reception of such alternate 120 and 7 5 code rates, causes the signal receiving such codes to alternately display Y/Y and Y/R indications; while at the same time the track section in the rear has a 180 code applied to it. Thus, in this form of the invention two approach signals are caused to give a distinctive indication under brokendown joint conditions, but due to the characteristics of the organization such conditions cannot be cascaded to the subsequent track sections in the rear.

This form of the invention also provides the same features of operation with respect to the passage of a short train as provided in connection with Fig. 1, since contacts of the relays H are included at all times in the code rate selecting circuits of the code transmitting relays. These H relays, as previously explained, drop away within a reasonably short time after a code ceases to be received, and such time is sufficiently short to insure that a passage of a short train will not result in the momentary transmission in the rear of that trainof a code rate higher than the most I restrictive code rate.

7 Having thus described two forms of a coded track circuit signaling system as embodying the present invention, it is desired to be understood that these forms are selected to facilitate in the disclosure of the invention rather than to limit the number of forms which it may assume; and, it is to be further understood that various modifications, adaptations and alterations may be applied to the specific forms shown to meet the requirements of practice, without in any manner departing from the spirit or scope of the present invention except as limited by the appended claims.

What I claim is:

1. In a coded track circuit organization for adjoining track sections separated by insulated joints, a code following track relay of the twoposition polarized type for the forward track section, a transmitter relay for applying polarized code pulses to the rear track section, coding means effective while said forward track section is occupied by a train and said track relay is inactive for intermittently operating said transmitter relay to provide a caution control code for the rear track section, and means responsive to the initial intermittent operation of said track relay when said forward track section becomes unoccupied subsequent to said track relay having been inactive for stopping operation of said transmitter relay by said coding means and for operating said transmitter relay in accordance with the operation of said track relay for a limited time after the intermittent operation of said track relay is first started, whereby failure of the insulated joints is detected by an abnormal operation of said track relay for a limited time if it should be operated by coding in the rear track section.

2. In a coded track circuit signalling system, two adjoining track sections separated by insulated joints and having a signal governing train movement from the rear track section into the forward track section, a code following track relay of the two-position magnetic stick type for the forward track section, code transmitting means for the rear track section for applying code pulses of opposite polarities alternately, code responsive relay means energized only in response to the repeated operation of said track relay for governing the indications of said signal,

circuit means governed by said code responsive relay means in a deenergized condition for causing operation of said code transmitting means at a particular code rate, and circuit means governed by said code responsive relay means in an energized condition for controlling said code transmitting means to apply code pulses of a rate corresponding to the rate of operation of said code following track relay, said circuit means being effective to hold said code transmitting means in one position for a limited time if the operation of said code following track relay is then responding to the code pulses being applied to said rear track section by said code transmitting means due to a failure of said insulated joints, whereby continuous coding operation of the track relay for the forward track section by operation of the transmitting means for the rear track section is prevented if the intervening insulated joints are broken down.

3. In a coded track circuit signalling system for railroads, the combination with two adjoining track sections separated by insulated joints and having a signal governing train movement from the rear track section into the forward track section, a code following track relay for the forward track section, a code response signal control relay V i8 energized only by the intermittent operation of said track relay for governing the indications of said signal, means effective while said signal control relay is deenergized for applying code pulses to the rear track section, and means effective for a limited time after energization of said signal control relay for energizing said rear track section at intervals corresponding with the periodicity of operation of said track relay for the forward track section.

4. In a coded track circuit signalling system of the character described, a forward track section and a rear track section separated by insulated joints, a two-position code following track relay for the forward track section, a transmitter relay for applying code pulses to the rear track section of such a character as would operate said track relay to its opposite positions if said insulated joints were broken down, a code responsive relay energized only in response to the repeated intermittent energization of said track relay, an operating circuit for said transmitter relay for the rear track section including in series contacts of said track relay and a front contact of said code responsive relay for operating said transmitter relay to a position corresponding to the position of said track relay, and circuit means including a code oscillator for intermittently energizing said transmitter relay to its opposite positions for a caution code while said code responsive relay is deenergized, whereby said track relay is maintained operated for a time until the code responsive relay is released if the track relay for the forward track section should happen to be made responsive to coding in the rear track section due to failure of the insulated joints.

5. In a coded track circuit signalling system two adjoining track sections separatedby insulated joints, a transmitter relay for applying code pulses to the rear track section, a code following track relay for the forward track section, a signal control relay energized only in response to the repeated intermittent energization of said track relay, coding contacts intermittently operated in accordance with the code for giving a clear signal indication, circuit means including a slow acting repeater relay of said signal control relay for rendering said coding contacts effective to control said transmitter relay after an interval of delay following the energization of said signal control relay, and circuit means governed by said signal control relay and its slow acting repeater relay for operating said transmitter relay in accordance with the periodicity of operation of said track relay during said interval of delay.

6. In a coded track circuit signalling system for railroads, two adjoining track sections separated by insulated joints, a signal governing train movement from the rear track section into the forward track section, a code transmitter relay for applying current pulses to the rear track section, a code following track relay for the forward track section, a signal control relay energized only by the intermittent operation of said track relay, a slow release repeater relay governed by said signal control relay, an operating circuit for said transmitter relay including a contact of said track relay and a front contact of said signal control relay, coding contacts operated intermittently in accordance with the codefor a clear signal indication, and another operating circuit for said transmitter relay including said coding contacts and a front contact of said repeater relay.

'7. In a coded track circuit signaling system for railroads, two adjoining sections of track separated by insulated joints, a signal for governing train movement from the rear track section into the forward track section, a code transmitter relay for applying code impulses of current to the rear track section. a code following track relay responsive to code impulses in the forward track section, a signal control relay governed by the operation of said track relay to thereby assume an active position While said track relay is receiving code impulses and to assume an inactive position when said track relay ceases to receive code impulses, a slow acting repeater relay energized only while said signal control relay is in an active position, an operating circuit for said transmitter relay for causing it to be operated at one code rate while said signal control relay is in an inactive position but to repeat the code impulses received by said track relay while said signal control relay is in an active position and said repeater relay has not yet picked up, and another operating circuit for said transmitter relay for causing it to be operated at a different code rate when said signal control relay is in an active position and said repeater relay is picked up, whereby in the event of the breaking down of said insulated joints, said transmitter relay is intermittently rendered active to transmit code pulses at said one code rate and said signal control relay is rendered active and inactive alternately with a periodicity too rapid to effect the picking up of said slow acting repeater relay.

8. In a coded track circuit signaling system for railroads, two adjoining track sections separated by insulated joints, a signal for controlling traffic over said forward track section from said rear track section, a code transmitter relay for applying code pulses to the rear track section, a code following track relay for the forward track section, a signal control relay energized only in response to the repeated operation of said track relay, a slow acting repeater relay energized only while said signal control relay is energized, means for rendering said code transmitter relay effective to transmit one code while said signal control relay is deenergized and to transmit a different code while said signal control relay and said slow acting repeater relay are both energized, and means for preventing the deenergization of said signal control relay from interrupting the transmission of said different code by said code transmitter relay while said repeater relay is picked up unless a train is in approach to said signal.

9. In a coded track circuit signaling system for railroads, two adjoining track sections separated by insulated joints, a signal for governing traffic over said forward track section from said rear track section, a code transmitter relay for applying code pulses to the rear track section, a code following track relay responsive to the presence of code pulses in the forward track section, a signal control relay energized only in response to the repeated operation of said track relay, a slow acting repeater relay energized only while said signal control relay is energized, control circuit means for said code transmitter relay governed by said signal control relay and said slow acting repeater relay so as to be effective to transmit one code while both of said relays are deenergized and to transmit a different code while said repeater relay is energized, and means effective upon the deenergization of said signal control relay for preventing the transmission of said different code when a train is in approach to said signal.

10. In coded track circuit signaling system for railroads, two adjoining track sections separated by insulated joints, a signal for governing traffic over the forward track section from the rear track section, a code transmitter relay for applying to the rear track section a code pulse of one polarity when in its one position and a code pulse of the opposite polarity when in its opposite position, a code following track relay of the polarized twoposition type responsive to code pulses of opposite polarities alternately in the forward track section, a signal control relay energized so as to be picked up only in response to the repeated operation of said track relay, a slow acting repeater relay energized only while said signal control relay is picked up, and control circuit means for said transmitter relay governed by said signal control relay and said slow acting repeater relay and effective to operate said transmitter relay to its opposite positions alternately at one code rate while both of said relays are de-energized and at a different code rate while both of said relays are energized, but acting while said signal control relay is energized and said repeater relay has not yet picked up to cause said transmitter relay to operate to its opposite positions by the operation of said code following track relay to its opposite positions in response to a code in the forward track section for applying that polarity of code pulse in the rear track section for each operation corresponding to the polarity of the code pulse in the forward track section causing that operation, whereby in the event of failure of said insulated joints any current flowing through said track relay from said rear track section tends to hold it in its existing position.

11. In a coded track circuit signaling system for railroads, two adjoining track sections separated by insulated joints, a signal for governing traffic over the forward track section from the rear track section, a code transmitter relay for applying code pulses to the rear track section when operated to its opposite positions, a code following track relay operated to its opposite positions by code pulses in said forward track section, a signal control relay energized so as to be picked up only in response to the repeated operation of said track relay, a slow acting repeater relay energized only while said signal control relay is picked up, control circuit means for said transmitter relay governed by said signal control relay and said slow acting repeater relay and effective to operate said transmitter relay to its opposite positions at one code rate when both of said relays are deenergized and at a different code rate when both of said relays are picked up, but acting while said signal control relay is picked up and said repeater has not yet picked up to cause said transmitter relay to be operated to its opposite positions by the operation ofsaid track relay to its opposite positions in response to a code in the forward track section, and circuit means governed in accordance with the approach of a train in th rear track section and its passage into the forward track section to cause said transmitter relay to transmit said one code rate when said signal control relay is dropped away and said repeater relay has not yet dropped away but acting when there is no train in approach to said signal to cause said transmitter relay to be operated to its opposite positions at said different code rate until said repeater relay drops away independently of the prior dropping away of said signal control relay.

12. In a coded track circuit signaling system for railroads, two adjoining track sections separated by insulated joints, a signal for governing traffic over the forward track section from the rear track section, a code transmitter relay for applying code pulses to the rear track section, a code following track relay responsive to the presence of code pulses in the forward track section, a signal control relay picked up in response to the repeated operation of said track relay, a slow acting repeater relay energized only when said signal control relay is picked up and being slow to pick up and drop away in response to its energization and de-energization respectively, a control circuit means for said code transmitter relay governed by said slow acting repeater relay so as to be effective to transmit code pulses at one code rate when said repeater relay is deenergized and to transmit code pulses at a different code rate while said repeater relay is picked up, a slow acting approach control relay associated with said signal and governed to indicate the presence and absence of a train in the rear track section, and means effective upon the drop away of said signal control relay to interrupt said control circuit means to stop the transmission of said different code even though said repeater relay is still picked up but said means being effective only if said approach control relay indicates the presence of a train in the rear track section.

13. In a coded track circuit organization for adjoining track sections separated by insulated joints, a two-position polarized code following track relay for the forward track section, decoding apparatus operated only when said track relay is receiving code pulses, a transmitter relay for applying polarized code pulses to the rear track section, coding means governed by said decoding apparatus and effective while said forward track section is occupied by a train and said track relay is inactive for intermittently operating said transmitter relay to provide a caution control code of polar impulses of opposite polarities alternately for the rear track section, circuit means governed by said decoding apparatus in response to the initial intermittent operation of said track relay when said forward track section becomes unoccupied and code pulses are applied thereto for stopping operation of said transmitter relay by said coding means and effective to operate said transmitter relay in accordance with the operation of said track relay to apply code pulses of the same polarity as those to which said track relay is then responding for only a limited time after the intermittent operation of said track relay is first started, whereby failure of the insulated joints applies pulses of such polarity to the forward track section as to cause the cessation of operation of said track relay for a limited time if its operation is being effected by code pulses from the rear track section, and other coding means governed by said decoding apparatus for operating said transmitter relay to provide a clear code of polar impulses of opposite polarities alternately for the rear track section after said limited time only if said track relay has continued its operation during such limited time.

FRANK X. REES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,342,488 Preston Feb. 22, 1944 2,357,518 Judge Sept. 5, 1944 

